Tyrannosaurus rex – All Nine Tons of It

A joint US and UK research team using sophisticated, three-dimensional laser mapping have calculated that tyrannosaurs were heavier than previously thought.  Using tyrannosaur fossil skeletons, including that of “Sue” the most complete Tyrannosaurus rex (and the biggest) found to date the scientists concluded that these Late Cretaceous predators could reach weights of up to 9 tons.

Tyrannosaurus rex

Using three-dimensional laser scans and computer modelling, British and U.S. scientists “weighed” five tyrannosaur specimens, including the Chicago Field Museum’s “Sue.  They concluded that Tyrannosaurus rex grew faster and weighed more than previously thought.  The discovery of sub-adult specimens in recent years has enabled palaeontologists to understand a little more about the ontogeny (growth) of these theropods, for example, it is now widely accepted that just like us humans, Tyrannosaurus rex underwent a growth spurt in its teenage years.

New Body Mass Estimates for Tyrannosaurus rex

Estimates of up to 9 tons in weight. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Remarkable Growth Rates of Dinosaurs

A number of studies have been published in recent years, providing evidence on the remarkable growth rates of different dinosaurs.  One recent study focused on the ontogeny of hadrosaurs (duck-billed dinosaurs), animals that were on the menu for the tyrannosaurs.  This study suggested that the herbivorous hadrosaurs actually grew faster than the predators, a strategy for survival when being small and young meant being a potential dinner for a hungry T. rex.

To read this article: Duck-Billed Dinosaurs Grew Up Fast to Avoid Being Eaten.

In the light of this Anglo/American research which suggests that T. rex may have been up to thirty percent bigger than previously estimated, so of these older papers may have to be revisited.

In an interesting twist to the T. rex growing fast and enormous research, the scientists have estimated that the smallest and youngest specimen of a Tyrannosaurus rex known, actually weighed less than previously thought.  This study indicates that T. rex grew more than twice as fast between 10 and 15 years of age as suggested in a study five years ago.  The University of California (Berkeley) conducted research into the growth of another dinosaur genus, an ornithopod called Tenontosaurus.  This research team concluded that dinosaurs may have reached maturity earlier than previously expected, their work, which involved studying the growth rings preserved in fossilised dinosaur limb bones suggested that dinosaurs did grow up fast, perhaps another survival strategy in the brutal Mesozoic.

University of California research into dinosaur growth: Dinosaurs Grew Fast, Lived Fast and Died Young.

The study, published in the online scientific journal PLoS One, (Public Library of Science) was conducted by a team of scientists led by Professor John R. Hutchinson of The Royal Veterinary College, London, and Peter Makovicky, PhD, curator of dinosaurs at The Field Museum of Natural History in Chicago.  “Sue” the biggest Tyrannosaurus rex is housed at the Chicago Museum.

According to Professor Hutchinson, who commented on the spurt growth of Tyrannosaurus rex during its teens:

“T-rex grew at 3,950lbs per year (1,790 kg) during the teenage period, which is more than twice the previous estimate.”

However, these predators sacrificed speed for power and strength as they got bigger according to this study.  The researchers concluded that heavy, adult Tyrannosaurus slowed down as they grew, but speeds around fifteen miles an hour, about as fast as a footballer can run were still possible.

The velocity that these animals could achieve slowed as they got bigger because the tyrannosaur torso became longer and heavier while its limbs grew relatively shorter and lighter, shifting its centre of balance forward.   This relates to an aspect of ontogeny studies called “distal growth”, it also explains why young animals have proportionately longer limbs than adults, try comparing a foal to its mother and you will see the difference in body proportions.

Professor Hutchinson added:

“The total limb musculature of an adult T. rex probably was relatively larger than that of a living elephant, rhinoceros, or giraffe, partly because of its giant tail and hip muscles.  Yet the muscles of the lower leg were not as proportionately large as those of living birds, and those muscles seem to limit the speed at which living animals can run.”

When commenting on the growth spurts of these apex predators, during their teenage years, Professor Hutchinson stated:

“At their fastest, in their teenage years, they were putting on 11 pounds or 5 kilograms a day.  Just think how much meat that is.  That’s a hell of a lot of cheeseburgers … it’s a whole lot of duck-billed dinosaurs they needed to be chowing down on.”

High Demands for Food

Such high demands for food to fuel their rapid growth may have had an impact on tyrannosaur behaviour.  A huge appetite would suggest that each T. rex or tyrannosaur group would need a massive territory to hunt in.  Each animal would need access to a substantial amount of potential prey – so as one spokesperson for Everything Dinosaur put it:

“Tyrannosaurs may have been few and far between.”

The rapid teenage growth spurt also suggests these reptiles must have had a high metabolic rate, fuelling the idea they were endothermic (warm-blooded).

The researchers, led by Professor Hutchinson and Dr Makovicky used scans of skeletons to build digital models and then added flesh using the structure of soft tissues in birds and crocodiles as a guide.  A number of composite models were then developed, to provide a spread of potential body masses, computer models to assess the body mass of less muscular dinosaurs and models to look at the maximum musculature that these skeletons could theoretically support.

One of the problems the team encountered was that the fossilised bones of many tyrannosaurs, including those of “Sue” from the Field Museum (Chicago) had been compressed during the fossilisation and preservation process, so assessments of the actual “life-size” of bones had to be calculated before an assessment of body mass could be carried out.  The study is further complicated by the fact that scientists believe that male and female tyrannosaurs had very different body forms.   It has been suggested that the more robust, bigger specimens represent females, smaller more gracile forms are males.   Female tyrannosaurs are believed to have been larger as they needed wider hips to allow the storage and passage of eggs.  Such dimorphism is common in Aves – close relatives of theropod dinosaurs.

For models and replicas of tyrannosaurs and other theropod dinosaurs: Tyrannosaur Models and Theropod Figures (Wild Safari).

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